1. Field of the Invention
This invention relates broadly to surgical instruments. More particularly, this invention relates to a surgical snare instrument for excising polyps.
2. State of the Art
Surgical snares instruments are used for the endoscopic removal of hypertrophic tissue growths within a body cavity, and particularly within the colon. Snare instruments generally include an elongate tubular member, such as a catheter sheath, a shaft extending through the tubular member, and an elastic wire (e.g., stainless steel or Nitinol) forming a loop movable distally and proximally within the tubular member. The loop can be opened by moving the loop beyond the distal end of the tubular member and closed by retraction into the tubular member, each effected by movement of the shaft relative to the sheath. A handle is provided at the proximal end of the instrument to facilitate this movement.
With the loop of the snare instrument in a retracted position, the distal end of the instrument is inserted through an endoscope into the gastrointestinal tract and moved toward a polyp or other tissue growth which is identified for removal from the wall of the tract. The handle of the instrument is then operated to expand the loop of the snare and an attempt is made to maneuver the loop to surround the polyp. If successful, the loop is then constricted about the polyp to excise it. Additionally, the snare instrument may be provided with cautery capability in order to limit bleeding and thereby enhance the polyp removal procedure.
It will be appreciated that manipulation of the loop of the snare instrument about the polyp is a difficult, and sometimes unattainable, task. The expanded snare loop often lies in a plane which is not conducive for maneuvering about the polyp along the colon wall. However, as the snare instrument is extended through a relatively central lumen of an endoscope to the locus of the polyp, and as the endoscope may be positioned centrally within the colon, it is difficult to direct the loop of the snare along the wall of the colon to ensnare the polyp. Therefore, the desired polyp retrieval often requires extensive effort and at times cannot be achieved with the snare instrument and a more invasive procedure may be required to remove the hypertrophic growth.